(a) Field of the Invention
The present invention relates to a field emission display, and more particularly, to a field emission display that includes a thin metal layer formed on a phosphor screen, which is provided on a faceplate, to improve brightness and contrast.
(b) Description of the Related Art
In a conventional field emission display (FED), there are formed on a backplate emitters that are electron emission sources, and electrodes (i.e., cathode electrodes and gate electrodes) that operate such that electrons are emitted from the emitters. A phosphor screen is formed on a surface of a faceplate opposing the backplate.
With this configuration, a difference in potential between the cathode electrodes and the gate electrodes is used to effect the emission of electrons from the emitters. The emitted electrons strike the phosphor screen to illuminate phosphors thereof, thereby realizing the display of predetermined images.
In order to attract the electrons emitted from the emitters toward the phosphor screen, a high potential state of the surface of the faceplate on which the phosphor screen is formed must be maintained. To realize this in the conventional FED, a transparent conductive layer (typically, an ITO layer) is formed between the faceplate and the phosphor screen, and an anode voltage of a few hundred to a few thousand volts is applied to the transparent conductive layer.
There have been efforts to improve screen brightness and contrast by adding to the above basic structure a thin metal layer (generally an aluminum layer), which is formed on the phosphor screen. U.S. Pat. No. 5,986,398 discloses an FED using such a structure.
With the formation of a thin metal layer on the phosphor screen, in addition to improvements in screen brightness and contrast resulting from a metal black of the metal layer, the anode voltage may be directly applied to the metal layer and the transparent conductive layer need not be included in the structure. As a result, a greater brightness may be realized since a higher anode voltage may be applied to the metal layer than to the transparent conductive layer.
FIG. 7 is a partial sectional view of a conventional FED. Phosphor screen 3 and metal layer 5 are formed on one side of faceplate 1. Anode voltage Va is applied to metal layer 5 during operation. Metal layer 5 extends past sealant 7 for connection to an external circuit (not shown). Sealant 7 is positioned on metal layer 5 and seals faceplate 1 and backplate 9.
However, there are problems associated with metal layer 5, and in particular, with metal layer 5 made of aluminum. That is, although an adhesive strength of metal layer 5 is exceptional immediately following a layer forming process such as sputtering, if thermal deformation occurs as a result of a baking process following sputtering, the adhesivity of metal layer 5 is significantly reduced. Accordingly, metal layer 5 having undergone a baking process is easily separated from faceplate 1 such that it is unable to perform its function. This makes metal layer 5 unsuitable for use as a terminal that receives the anode voltage.
Further, the strength of metal layer 5 is reduced for the above reasons such that metal layer 5 is damaged in the vicinity of sealant 7. This reduces the degree of vacuum in the FED, negatively affecting the overall operation of the display.